The long-term goal of our research is to achieve a global and mechanistic understanding of the process by which proteins transiting the endoplasmic reticulum (ER) are recognized and targeted for degradation. The ER is responsible for the folding, modification, and trafficking of approximately one-third of the cellular proteome, including integral membrane proteins that are presented on the cell surface (e.g. channels and receptors) and soluble proteins that are secreted (e.g. growth factors and extracellular proteases). The quality of the proteins that are deployed from the ER is tightly monitored and controlled by a system now known as ER-associated degradation (ERAD). ERAD employs an extensive network of components that mediate misfolded protein detection, dislocation into the cytoplasm, ubiquitination, and proteasomal degradation. In addition to its role in the clearance of misfolded proteins (i.e. quality control), ERAD also regulates the abundance of proteins (i.e. quantity control) to modulate important cell biology processes. For example, ERAD mediates the sterol- dependent degradation of enzymes necessary for cholesterol synthesis, HMG CoA reductase and squalene monooxygenase. Due to the lack of global methods to study ERAD, our understanding of the pools of endogenous substrates that are degraded by different ERAD pathways remains limited. To overcome this obstacle, we developed a VCP-inhibitor substrate trapping approach (VISTA) to identify endogenous ERAD substrates. In our proposed research we will apply this unique strategy to: 1) define pathway-specific ERAD substrates and 2) identify metabolically regulated ERAD substrates. Our studies will characterize a new method of broad utility to the biomedical research community and will advance our understanding of the role of ERAD in cellular protein homeostasis.